docker初始化时会下载 boot2docker.iso 文件，但是下载太慢了，导致下载失败。

报错：

Error with pre-create check: "read tcp 192.168.43.151:49696->52.216.176.107:443: wsarecv: A socket operation was attempted to an unreachable network."
Looks like something went wrong in step ´Checking if machine default exists´... Press any key to continue...

这里我下载好备份一下，以防以后要用。

boot2docker.iso

下载好后放到C:\\Users\\hjw\\.docker\\machine\\cache文件夹里面就行了。